In the production of clinker, the energy expenditure involved in the precalcination or calcination of the charge constitutes an essential cost factor. As a rule, precalciners require more than 60 percent of the overall heat input in such plants, wherein the clinker enters a clinker cooler after having left the rotary tubular kiln or clinker kiln. Such clinker coolers use ambient air, i.e. comparatively cold air, for cooling, with considerable amounts of cooling air being consequently heated. Precalciners require relatively high amounts of combustion air, wherein the use of preheated air is especially favorable in terms of energetics. To this end, clinker furnaces which are preceded by precalciners usually comprise what is called a tertiary air duct to feed the exhaust air from the hot zone of the clinker cooler back to the precalciner as combustion air.
In order to achieve optimum operating characteristics in such a plant, the amount of air respectively fed to the calciner must, however, be adjusted, via tertiary air ducts, as a function of the amount of fuel used, wherein exhaust air having a temperature of between 650 and 1100° C. and a high portion of clinker dust can, as a rule, be drawn off the clinker cooler. The gas regulators or throttle valves usually provided there are subject to extremely high wear due to the high temperatures and the high dust load, so that plants of this type have to be repeatedly shut down for maintenance purposes in order to service or exchange the throttle valves.
DE 102006023980 A1, for instance, describes a throttle valve which is formed of an element that is rotationally or pivotally mounted in a calciner nozzle to adjust the cross section of the calciner nozzle.
US 2002022207 A1 describes a pivotable throttle valve which is arranged in an exhaust gas duct of a rotary tubular kiln and capable of being pivoted into the exhaust gas duct from a laterally attached fulcrum, wherein the exhaust gas flow flows laminarly in any pivoted position.